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14. Knochenhaurer’s Experiments. Conducting Power of Gas. Spark. Penetrating Power. Relation of E. M. F. to Pressure of Gas. 1834. Pogg. Ann., Vol. LVII., and Gordon, Vol. II. Boltzmann’s experiment (Pogg. Ann., CLV., ’75), and calculation indicated that a gas at ordinary pressure and temperature must have a specific resistance at least 10²⁶ times that of copper. Pogg. Ann., CLV., ’75. Sir William Thomson (Kelvin) confirmed this limit for steam, and Maxwell the same for mercury and sodium vapor, steam and air. From Maxwell’s MSS. Herwig was not sure but that the Bunsen burner flame and mercury vapor conducted. He allowed for the conductivity of the walls of the glass container. Braun treated of the conductivity of flames. Pogg. Ann., ’75.

14a. Varley found that 323 Daniel cells only just initiated a current through a hydrogen Geissler tube, and only 308 cells continued the current after once started. Knochenhaurer found that Harris’ (Phil. Trans., 1834) law did not hold exactly true, and that the ratio between the E. M. F. and the air pressure becomes greater and greater as the pressure becomes less and less. Harris thought the ratio was constant. The limits of his pressures were from 3 to 27.04 inches of mercury. Stated in other words, his results were the same as those of Harris and Masson (Ann. de Chimie, XXX., 3rd Se.), except that a small constant quantity should be added. ssss1.